Recently, the use of bag less vacuum cleaners, that is vacuum cleaners which do not make use of disposable dust bags, has increased. Dust from the dust laden airstream which is sucked into the vacuum cleaner is separated in a dust separation chamber and collected in a dustbin, which must be frequently emptied by the user. As long as the dust level in the dustbin is below a critical level, normal functionality of the dust separation in the vacuum cleaner is provided. However, a common problem for bag less vacuum cleaners is that the user forgets to empty the dustbin before the critical level is reached, which results in unnecessary clogging of filters and other parts of the vacuum cleaner. The consequences of this are loss of cleaning performance and increased amount of maintenance of e.g. the main filter and filter screen. Thus, there is a need for indicating to the user when it is time to empty the dustbin before the critical level is reached.
It is known to arrange optical dust indicators in vacuum cleaners for the purpose of detecting dust. The optical dust indicators are typically based on optical sensors providing a detections system, such as a light emitter in combination with a light receiver, which are arranged such that when dust is present in the optical path of the optical signal provided by the light emitter, the light detector detects a decreased or blocked light signal. The optical dust indicators are sensitive to dust getting stuck somewhere in the optical path of the detection system, as this blocks the light signal.
A dust detector utilized in a vacuum cleaner to indicate the amount of dust in a dust laden air stream is disclosed in U.S. Pat. No. 5,163,202. The dust detector is arranged in a suction passage in fluid contact with e.g. a floor nozzle of the vacuum cleaner. A light-emitting element and a light-detecting element, are arranged in a respective opening. The openings are diametrically oppositely arranged in the suction passage wall. The light-emitting element and the light-detecting element are arranged in optical communication and dust is detected when being present in the optical path of the detection system. Further, air passages guarded by pressure responsive valves are defined in the suction passage wall. These are arranged for introducing ambient air into the suction passage via the openings during operation of the vacuum cleaner. The pressure difference created between the ambient space and the suction passage during operation of the vacuum cleaner activates the valves and ambient air flushes over the light-emitting element and the light-detecting element, thereby keeping them free from dust-particles which may otherwise contaminate them. The known dust detector is quite complicated as it comprises a plurality of mechanically complex, moving constituents.
Thus, there is a need within the art for an optical dust indicator for indicating the dust level in a dustbin. In particular, it would be advantageous to have an optical dust indicator which constitutes only fixed parts and which prevents from contamination caused by dust-particles in areas overlapping its optical path.